1. Field of the Invention
The present invention relates to a therapeutic and/or preventive agent for neurodegenerative diseases such as Alzheimer's disease and amyotrophic lateral sclerosis.
2. Description of Related Art
Neurodegenerative diseases are caused by the selective death (apoptosis) of particular neurons, triggered by characteristic abnormal protein accumulation in the neurons and so on. In some cases of neurodegenerative diseases, genetically defined abnormalities contribute to the development of the disease. The neurodegenerative diseases here include cerebral degenerative disease (e.g., Alzheimer's disease, Parkinson's disease, progressive supranuclear palsy, and Huntington's disease) and spinal degenerative disease/motor neuron degenerative disease (e.g., amyotrophic lateral sclerosis and spinal muscular atrophy).
Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease with selective loss of motor nerves in the cerebrum, brain stem, and spinal cord that typically affects people of middle or advanced age (Cleveland D W and Rothstein J D, 2001, Nat Rev Neurosci 2: 806-819; and Hand C K and Rouleau G A, 2002, Muscle Nerve 25: 135-159). ALS causes muscular atrophy and muscular weakness in voluntary muscles in the whole body except for extraocular muscles and eventually causes respiratory failure. Patients suffering from ALS usually die in 3 to 5 years from the onset.
Riluzole is the sole drug previously approved for ALS in US and Japan. Riluzole was originally developed as an anticonvulsant inhibiting glutamate release and has been reported in several clinical trials to exhibit only slight efficacy for the survival of ALS patients (Rowland L P and Shneider N A, 2001, N Engl J Med, 344, 1688-1700; and Turner M R and Parton M J, 2001, Semin Neurol 21: 167-175). In addition to riluzole, various factors including ciliary neurotrophic factor (CNTF) and insulin-like growth factor I (IGF-I) were tested in clinical trials and however, fell short of success (Miller R G et al., 1996, Ann Neurol 39: 256-260). Thus, there are currently no therapeutic agents effective for ALS under present circumstances.
Approximately 10% of ALS cases are familial (FALS) and with mostly autosomal-dominant inheritance. In 1993, Rosen et al identified for the first time the superoxide dismutase-1 (SOD1) gene located on the chromosome 21 as a causative gene by the analysis of pedigree with autosomal inheritance (Rosen D R, et al., 1993, Nature 362: 59-62). Approximately 20% of FALS cases are caused by mutations in the SOD1 gene, and most of these mutations are missense point mutations. More than one hundred SOD1 mutations have been found to cause FALS (Cleveland D W and Rothstein L D, supra). Several groups have reported that overexpression of FALS-associated SOD1 mutant genes induces neuronal cell death in vitro (e.g., Rabizadeh S, et al., 1995, Proc Natl Acad Sci USA 92: 3024-3028; Durham H D et al., 1997, J Neropathol Exp Neurol 56: 523-530; and Ghadge G D et al., 1997 J Nerosci 17: 8756-8766). Besides this, the activation of caspase-3 has been observed in the spinal cords in ALS patients. Taken altogether, the inhibition of neuronal cell death is an effective way for the development of therapeutic agents for ALS.
In addition to CNTF and IGF-I described above, Bcl2, a non-specific caspase inhibitor zVAD-fmk (Kostic V, et al., 1997, Science 277: 559-562; Azzouz M, et al., 2000, Hum Mol Genet. 9: 803-811; and Li M, et al., 2000, Science 288: 335-339), and alsin, the newly identified product of the ALS2 gene whose missense mutations cause recessive-inherited FALS (Kanekura K, et al, 2004, J Biol Chem 279: 19247-19256), have been reported to antagonize neuronal cell death caused by the overexpression of SOD1 mutants.
Alzheimer's disease (AD) is clinically characterized by progressive amnesia and cognitive impairment, and pathologically by extensive neuronal loss, intraneuronal tangles, and extracellular senile plaques whose cores have a high affinity to Congo red. There are no effective therapies for AD. It has been generally accepted that the clinical manifestation of this disease can be mostly explained by progressive neuronal cell death. Therefore, it is essential for the development of effective therapies against AD to elucidate the mechanisms underlying neuronal cell death in AD.
There are three different genes whose mutations cause early-onset familial AD (FAD). Three genes encodes APP (APP refers to amyloid precursor protein APP695), presenilin (PS)-1, and PS2 (Shastry, B S and Giblin, F J, 1999, Brain Res. Bull. 48: 121-127). Yamatsuji et al have indicated that three FAD-linked APP mutants with mutations on the V642 positions cause neuronal death (Yamatsuji, T et al., 1996, Science 272: 1349-1352). This notion was verified by several groups that performed similar experiments using primary cultured neurons or other neuronal cell lines (Zhao, B et al., 1997, J. Neurosci. Res. 47: 253-263; and Luo, J et al., 1999, J. Neurosci. Res. 55: 629-42). In addition, Wolozin et al found that expression of FAD-associated mutant N141I PS-2 significantly induced death of PC12 cells, and that expression of FAD-associated mutant PS-1 induces apoptosis in T lymphocytes (Wolozin, B et al., 1996, Science 274: 1710-1713; and Wolozin, B et al., 1998, Neurobiol. Aging 19: S23-27). It has also been observed that expression of FAD-linked PS-1 mutants sensitizes neurons to death caused by Aβ or lack of a trophic factor (Guo, Q et al., 1996, Neuroreport 8: 379-83; Zhang, Z et al., 1998, Nature 395: 698-702; and Guo, Q et al., 1999, Proc. Natl. Acad. Sci. USA 96: 4125-30), and that cultured cortical neurons derived from transgenic rats overexpressing wild-type PS-1 are more sensitive than non-transgenic controls to cell death caused by lack of a trophic factor (Czech, C et al., 1998, Neuroscience 87: 325-36). It has also been experimentally suggested that PS-1 mutants cause neuronal cell death (Weihl, C C et al., 1999, J. Neurosci. 19: 5360-9; and Bursztajn, S et al., 1998. J. Neurosci. 18: 9790-9). Thus, it is concluded that expression of all four types of FAD genes (V642 APP mutant, NL-APP, PS-1 mutant, and PS-2) induce neuronal cell death or sensitize neurons to death caused by other insults. Therefore, from the standpoint of neuronal death, the most important key for the development of AD therapies is to find a molecule that can suppress cell death induced by AD genes.
Huntington's disease (HD) is a neurodegenerative disease whose predominant manifestations consist of chronic progressive involuntary choreiform movements and dementia. Most HD cases are inherited in an autosomal-dominant fashion. Intellectual and psychiatric disorders seen in this disease are originated from extensive atrophy in the cerebral cortex, and pathological changes causing choreiform movements have been thought to be caused by atrophy of the corpus striatum, particularly by that of the nucleus caudatus. The HD pathogenesis has been investigated from the standpoint of amine metabolism and extrapyramidal syndrome in brain. A nucleotide sequence encoding polyglutamine on chromosome 4 provides a key to the HD pathogenesis. A glutamine-encoding triplet-nucleotide CAG is normally repeated 10 to 35 times (17 times on average). In HD cases, disease-causative proteins contain polygultamine regions consisting of 37 or more glutamines. Such abnormal proteins accumulate in neurons and promote cell death. Neurons in the corpus striatum are degenerated in HD. They include inhibitory neurons that originally send fibers to the substantia nigra or globus pallidus and release a neurotransmitter γ-aminobutyric acid (GABA) as well as excitatory neurons that send fibers to the same sites and release a neurotransmitter substance P. In addition, interneurons with short fibers in the corpus striatum, which use acetylcholine as a neurotransmitter, are partially degenerated. The degeneration of dopaminergic neurons projecting fibers from the substantia nigra to the corpus striatum causes the dysfunction of the extrapyramidal system. HD patients usually die of infectious disease or respiratory disorder accompanying dysphagia in 10 to 15 years since the disease onset.
ADNF or ADNF9 (activity-dependent neurotrophic factor), which consists of nine amino acid residues (Ser-Ala-Leu-Leu-Arg-Ser-Ile-Pro-Ala (SEQ ID NO: 5)), was originally purified by Gozes et al from the culture medium of astrocytes stimulated with VIP (Brenneman D E and Gozes I, 1996, J Clin Invest 97: 2299-2307; Brenneman D E, et al., 1998, J Pharmacol Exp Ther 285: 619-627; and Blondel O, et al., 2000, J Neurosci 20: 8012-8020). ADNF has been shown to protect neurons from neuronal cell death caused by some neurotoxic insults including amyloid β (Brenneman D E, et al., 1998, J Pharmacol Exp Ther 285: 619-627; and Glazner G W, et al., 2000, J Neurochem 73: 2341-2347). ADNF is a unique neuroprotective factor in that it has the neuroprotective activity at its lower concentrations from the femtomolar (fM) to picomolar (pM) order, and loses the activity at concentrations higher than the nanomolar (nM) order. Such unique but unfavorable property of ADNF have prevented it from being developed as an anti-Alzheimer's disease (AD) drug.
We have previously discovered a gene that encodes a 24-amino-acid peptide named Humanin (HN), using a cDNA library constructed from the brain tissues of AD patients. HN protects neurons from V642I APP-induced death. HN also suppresses all tested other types of neuronal cell death related to AD, that is, neuronal cell death induced by all known FAD genes and Aβ(1-43), while it does not show the rescue effect against neurotoxicity caused by polyglutamine repeats associated with Huntington's disease, spinocerebellar ataxia, or by amyotrophic lateral sclerosis-associated SOD1 mutants. We have further found that an HN derivative whose serine residue at the position 14 is replaced by glycine or D-serine has 1000-fold potent neuroprotective activity (International Publication No. WO 01/21787 A1; Hashimoto, Y et al., 2001, J. Neurosci., 21: 9235-9245; and Terashita, K et al., 2003, J. Neurochem., 85: 1521-1538).
Under these circumstances, we have conducted extensive studies to develop potent HN- and ADNF-derived therapeutic peptides protective against various neurodegenerative diseases, and have finally found a polypeptide named colivelin that is effective for the treatment of multiple neurodegenerative diseases including AD and amyotrophic lateral sclerosis.